Art of cracking hydrocarbon oils



- J. PERL ART OF'CRACKING HYDRocARoN oILs ,Filed NOV. 20. 1924 INVENTOR `fo/Ph 77er/ Q BY Nwe

ATTORNEY Patented Oct. 30, 192.8,

UNITED STATES 1,689,363 PATENT OFFICE.

JOHN PERL, or NEW Yonx, N. Y., vAssIeNoR To sINoLAm REFTNING COMPANY, or

CHICGOLILLVINOIS, A CORPORATION OF MAINE.

ART OF GRACKING HYDROCARBON OIJ/LS.

application iiiea November 2o, 1924. serial No. 750,993.

This linvention relates toiinprovements in cracking heavier hydrocarbon oils, such as gas oil, for the production of lighter -hydrocarbon oils, such as gasoline or pressure distillate, 'by distillationunder pressure. The invention includes improvements in both method and` apparatus.

When' a charge or' oil, such as gas oil, is subjected to a cracking temperature in a pressure still, cracking takes place in a progressive manner. Lighter constituents produced by the cracking operation are vaporized, and other constituents, s uch as heavierhydrocarbons formed by the cracking operation,niay remain and mix With the charge in the still. An amount of asphaltic or pitch-like constituents is also progressively formed. Initial,-

' lly, these pitch-like constituents inayremain more or less completely in solution in thestillcharge, but, as the crackingoperation proceeds and part of the charge is cracked and vaporized and additional amountsof the pitch-like constituents are formed, 'the concentrationof pitch-like constituents in the charge passes saturation and separation and precipitation of these constituents beeins. b Externally heated pressure stills having heat transferring walls of iron or steel arranged totransferheat from heating gases circulated about the exterior of the wall to a body of the oil in contact with' the interior of the wall' are commonly employed for carrying out the cracking operation The pitchlike constituents formed by the crackino' operation tendto deposit upon the metallic l eating Walls as they separate from the charge, and in some cases deposits may form upon the heating surfaces even When the general concentration of pitch-like constituents is below'saturation in the entire still charge. -This is apparently due to a preferential ailinity of the pitch-.like constituents, or of vsome component of the pitch-like constituents,

possibly sulphur' or son'iesulphur compounds,

for the highly heated metal of the heat-transferring Wall, or to a local increase inthe concentration of pitch-like,constituents iniin'cdately adjacent the heating wall..

These pitchy de iosits, or, the coky carbonaceous masses to Wliic'h they are rapidly'converted in contact With the hot heating Wall, are not good conductors of heat so'that a danger of overheating and failure of the frequent cleaning of the still, of course decreases the overall eiciency and capacity of the still. The cleaning operation,.likewise,

.is not Without its difliculties, particularly as in Contact with the hot heat-transferring Wall the deposit tends to bake to a hard, compact,

dense, carbonaceous mass closely adhering to the Wall.- The Wear due to the cleaning operation' and co-rrosion due to the deposits also necessitates replacement of the heattransferring' Walls from time to time.

According to the present invention, vthe hea-ting surface in contact with the oil is modied to provide a surface inhibiting the tendency o f the pitch-like constituents formed by the cracking operation to adhere thereto, Whether such constituents are in solution in thev 'still charge or precipitated therefrom, and circulation of the oil over the heating surface is maintained, so that such constituents are swept along with the oil and so lthat deposit of such pitch-like constituent-s orformation of closely adhering car- `bonaceous llayers on the heating surfaces isphur-conta-inin'g coating is provided upon the surfaces of the heating Walls of the pressure still which are in contact with the body of oil in the still. This .sulphur-containing coating may be applied vby passing hydrogen suliideover the iron or steel heating sur ace While heated to a dull red. The hydrogen suldemay also be diluted with some inert gas such as nitrogen, for example a mixture of equal volumes of nitrogen and hydrogen sulfide may be employed, to assist in the formation of a thin sulphurized coating on the heating surface. This sulphur-containing coating modifies the heating surface so that pitch-like constituents in solution or in suspeusion'fin the oil in contact therewith do not have the marked tendency to adhere to the surface exhibited in connection with or.- dinary iron or steel surfaces at the cracking temperature.

The sulphurized coating formed by treating the heating surface with hydrogen sulfide at an elevated temperature apparently consists of a thin film of metallic sulfides. The coating is thus formed by reaction between the hydrogen sulfide and the metal of the heating surface. This coating may be damaged or removed by cleaning operations, and may need to be renewed or repaired from time to time.A Sulphur-containing componnts of the voil may assist in maintaining the protective sulphurized coating, or a small amount of hydrogen sulfide may be passed over the heating surface during the progress of the cracking operation.

The invention is of special value and application in connection with cracking operations in which the concentration of pitchlike constituents in the pressure still charge is controlled and maintained below saturation by introducing fresh oil and withdrawing tar in regulated amounts during the progress of the cracking operationhin the manner described in an application vfEugene C. Herthel filed lSeptember 24, 1923 Serial No. 664,502. In connection with an operation of this type; and, by carrying out the cracking operation in a pressure still having heating surfaces with a sulphur-containing coating while maintaining the concentration of pitch-like constituents in the still charge below saturation by the regulated introduction of fresh oil and Withdrawal of body of oil is heated to the cracking temperature by heat transferred through the still shell. The invention is, however, of special value and application .in connection with pressure stills in which a circulation of the oil over the heating surfaces is maintained. In such stills, the sulphur-containing coating on the heating surfaces inhibits the tendency of the pitch-like constituents to adhere thereto and the circulation of the oil over the heating surfaces sweeps the pitch-like constituents along with the oil eliminating or reducing the formation of deposits thereon. Where the invention is employed in connection with a single-pass tubular pressure still, that'is a still in which the oil is forced once through one or more externally heated tubes, the sull I I phur-containing coating on the surfaces ofl the heating tubes in contact with the oil reduces the tendency o f pitch-'likev constituents to adhere to the tubes and the circulation of Lacasse the oil therethrough tends to carry such constituents along with the circulating oil so that they are discharged with the oil from the heating tubes.

The invention is of particular advantage in connection with pressure cracking stills in which the oil charge is circulated and recirculated over the heating surfaces. As compared to a single pass tubular cracking still, forexample, the pitch content of the oil in the still is also circulated and recirculated over the heating surfaces. In accordance with the present invention, however, the concentration of pitch-like constituents in the charge may be carried to a greater value before objectionable deposition of pitch and carbon on the heating surfaces begins in stills of this character. Thermosiphonic action may be relied on to maintain the circulation in such'stills, or mechanical forcing means, such as a pump, may, with advantage, be employed for maintaining a forced and rapid circulation of the oil over the heating surfaces. Opportunity may also be provided in suoli stills for the separat-ion, outside of the heater, of pitch-like Iconstituents carried through the heater with the circulating oil so that recirculation of such constituents through the heater ma be somewhat reduced.

The invention will e further described in connection with the accompanying drawings which illustrate, in a diagrammatic and conventional way, an apparatus embodying the invention and adaptedfor practicing the process of the invention. It is intended and will be understood, however, that this further description and illustration are for the purpose of eXempliication only and that the invention is not limited thereto but that it may be carried out in a great variety of apparatus.

The invention is, however, of special value andapplication in connection with a still of the character illustrated. This pressure still is of the general construction' and operation described in United States Letters Patent No. 1,285,200 granted to the Sinclair Refining Company November 19, 1918 on the application of Edward W. Isom.

The pressure still illustratedcomprises a bank of heating tubes 3 arranged in the heat- .ing Hue of a furnace, a bulk supply tank 4 located away from the furnacera circulating pump 5,and circulating connections 6,7 and8 'connecting successively the bulk supply tank,

thecirculating pump, the lower end of the heating tubes, and the upper end of the heating tubes and the bulk supply tank. Screw plugs 2 are arranged in the upper and lower headers of thetubular heater opposite the ends of-each of the heating tubes. Arranged above the hulkssupply tank is a reiuX tower9having baileatherein. The vapors from the bulk supply tank are discharged into the lower end of the reflux tower through the vapor line l0 A of the tubes in a similar way.

and reflux, together with any admixed fresh oil, is returned to the circulating connection 6 through the overflow reflux line 11. The vapors from the upper end of the reflux tower escape through the vapor line 12 t`o the condenser 13 which is arranged to discharge into the receiver 14. The condensed distillate is discharged through the valved outlet 15 and the uncondensed vapors and gases through the valved outlet 16. A feed line 17 is arranged for introducing fresh oil into the upper end of the reflux tower into direct contact with the vapors therein, and a tar line 18 is arranged for withdrawing tar during 1' the progress of the cracking operation.A A

connection 20 is provided for introducing fresh oil through the bearings of the circulating pump, and a connection 21 is arranged for initially charging `and for pumping out the still. The pressure may be reduced and regulated by a regulating valve 22 arranged between the reflux tower and the condenser or by valves located beyond the condenser.

v Each of the heatinor tubes 3 is provided internally with a sulphur-containing coating.

In a commercial still of the character illustrated, the heating tubes may consists of 4 cold-drawn mild-steel tubes. The sulphurcontaining coating may be applied to the interior surfaces of the tubes while in place in the still by heating them to the appropriate temperature by means of the still furnace and passing hydrogen sulfide, or a gas mixture including hydrogen sulfide, through the tubes. The sulphurizing gas may be introduced into one end of the tubes' by removing the plugs 2 and inserting an appropriate gas connection into the tubes through the openings and the waste gas may be removed from the other end The sulphurcontaining vcoating may be repaired or replaced in the same way. v

In one way of carrying out the process of the present invention in the apparatus illustrated, the still is charged, for example with gas oil, and brought to the desired cracking temperature and pressure in the usual'way. The vapors are then allowed to pass into the condenser and additionaly fresh charging stock is introduced into the upper end of the reflux tower. Some fresh oil is also introduced through the-bearings of the circulating pump while it is in operation to cool and protect them. Before the pitchcontent of the charge reaches the saturation point, the withdrawal of tar is begun, and the rateof introduction of fresh oil and withdrawal of tar is regulated to maintain the concentration of pitch-like constituents in the still charge below saturation. The invention is also useful in connection with processes in which no tar or only'a relatively small amount of tar is withdrawn, and by carrying out such operations in accordance with the present invention, the concentration of pitch-like constituents in the charge may be carried to a materially increased value before objectionable deposition begins.

It will thus be seen that this invention provides an improved method and apparatus for i era-tion in which the concentration of pitchlikecQnstit-uents in the charge is controlled by the-regula ted introduction of fresh oil and withdrawal of tar.

It will also be apparent that the present invention may be employed in conjunctionwith a great variety of cracking processes and that existing. cracking apparatus may readily be modified in accordance with the present invention.

Iclaim: e

1. In a pressure still for cracking hydrocarbon oils, a tubular heater, means for circulating heating gases externallyabout the tubular elements of the heater and means for circulating the oil therethrough, the internal surface of the tubular heater elements having an iron sulphide coating thereon.

2. vIn a pressure still for cracking hydroi carbon oils, a tubular heater, connections adapted for circulating and recirculating'a liquid body of oil in the still therethrough, and means for circulating heating gases externally about the tubular elements of the heater, the internal surface of the tubular heater elements having an iron sulphide coating thereon.

3. lIn a pressure still for cracking hydrocarbon oils, a tubular heater, connections including a mechanical forcing means adapted vfor circulating and recirculating a liquid body of oil in the still therethrough, and means for circulating heating gases externally `about the tubular elements of the heater, the internal surface of the tubular heater elements having an iron sulphide coating thereon. v I

4. A pressure still for cracking hydrocarbon loils, comprising a bulk supply tank and a heater having a surface with an iron sulphide coating'adapted for contact with oil in the still, means for externally heating the heater, and connections for circulating oil from the bulk supply tank to and through, the heater back to thebulk supply'tank.

y 5. In cracking hydrocarbon oils by distillation under pressure, the improvement which comprises heating a liquid body of the oil to the cracking temperature by heat transferred thereto through an externally lio heated wall having an iron sulphide coating in contact withthe oil. c

6.In cracking hydrocarbon oils by Ydistillation under pressure, the improvement which comprises circulating the .oil through a tubular heater having an internal surface in contact with thecirculating oil having an iron sulphide coating thereon, and heating the oil to the cracking temperature in the heater by externally applied heat.

7. In cracking hydrocarbon oils by -dis tillation undery pressure, the improvement which comprises-mechanically circulating the oil through a tubular heater having an inter-` nal surface in contact with the circulatingl oil throughout the cracking operation hav. ing an iron sulphide coating thereon, and heating theoil to the cracking temperature in the heater by externally appliedheat.

8. In cracking hydrocarbon oils by distillation under pressure, the improvement which comprises circulating the oil from and to a bulk supply tank through a heater, maintaining an iron sulphide coating on the surface of the heater in contact with the oil throughout the cracking operation, and heating the oil to vthe cracking temperature therein by externally applied heat.

9. In cracking hydrocarbon' oils by distillation under pressure, the improvement which comprises mechanically circulating the oil from and to a bulk supply 'tank through a heater, maintaining an iron sulphide coatingon the surface of the heater in cont-act with the oil throughout `the cracking operation, and heating the oil to the cracking temperature therein by externally applied heat.

l0. In cracking hydrocarbon oils by dis-` tillation under pressure, the improvement which comprises circulating the oil through a heater having an iron sulphide coating on the internal surface in Contact with the circulating oil, heating the oil to the cracking Lacasse temperature inthe heater by externally applied heat, promoting the separation of suspended constituents from the oil discharged from the heater externally of the heater, and recirculating the oil through the heater.

11. In cracking hydrocarbon oils by distillation under pressure, the improvement f lng surfaces having an iron sulphide coating in contact with the oil, 'heating the oil to the cracking-temperature by heat externally applied to the heating surfaces and controlling the concentration of pitch-like constituents in the body of oilv by adding fresh oil thereto and withdrawing tar therefrom.

13. In cracking hydrocarbon oils by distillation under pressure, the improvement which comprises circulating the oil over heating surfaces having an iron sulphide coating in contact with the oil and heating the oil to the cracking temperature by heat externally applied to the heating surfaces.

14. In cracking hydrocarbon oils by distillation under pressure, the improvement which comprises initially heat-ing a liquid body of the oil to the-cracking temperature by contact with an externally heated surface having an iron sulphide coating thereon and passing a small amount of hydrogen sulfide over the heating surface during the progress of the operation.

In testimony whereof I aiiix my signature.

JOHN PERL. 

